Oh ok thank you ladies! Makes sense now
Its when the egg is fertilized, but dies soon after implantation.
Agree with Lesley. To expand upon what she said, the reason they call it chemical pregnancy is because it's not technically a pregnancy. Basically the egg and sperm meet, and begin releasing chemicals that can sometimes be detected by a pregnancy test. BUT the egg never implants, which is when pregnancy "technically" occurs (because without implantation, the egg will be passed out of the uterus with a woman's period blood).
So it's a "chemical" pregnancy because the chemicals (hormones) for pregnancy are there, but not the actual pregnancy.
a chemical pregnancy is a very early MC, some women when testing too early(before their period) get a positive test result but then end up with there period... and not prego... so thats part of why they warn against testing too early too...